1. Field of the Disclosure
The disclosure relates to power converters, and more particularly, to control circuits for isolated power converters.
2. Background
Switch mode power converters are widely used in household or industrial appliances for converting a low frequency (e.g., 50 Hz or 60 Hz) high voltage alternating current (ac) input voltage to a required level of direct current (dc) output voltage. For example, switch mode power converters may be included in commonly used electronic devices, such as battery chargers for mobile electronic devices. Various types of switch mode power converters are popular because of their well regulated output, high efficiency, and small size along with their safety and protection features. Popular topologies of switch mode power converters include flyback, forward, boost, buck, half bridge, and full bridge, among many others including resonant types.
Switch mode power converters may include an energy transfer element, a power switch, and control circuits that operate to regulate the value of the power converter output voltage. The energy transfer element (e.g., a coupled inductor) may include a primary winding and a secondary winding that are galvanically isolated from one another. The primary winding may be coupled to circuits on the input side of the power converter, such as the power switch. The secondary winding may be coupled to circuits on the output side of the power converter that deliver the regulated output voltage to the electrical load.
The power switch (e.g., a high voltage power switch) may be coupled to the primary winding of the energy transfer element to control current through the primary winding. The control circuits of the power converter may sense the output voltage and control the state of the power switch to control the transfer of energy from the primary winding to the secondary winding in response to the sensed output voltage. Some of the control circuits (e.g., logic circuits) may operate at a relatively low voltage (e.g., at less than 5 V). Accordingly, the control circuits may also include components that regulate the operating voltage of the control circuits at a relatively low voltage.
Corresponding reference characters indicate corresponding components throughout the several views of the drawings. Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present disclosure. Also, common but well-understood elements that are useful or necessary in commercially feasible embodiments are often not depicted in order to facilitate a less obstructed view of the various embodiments of the present disclosure.